The present invention relates to a multilayer birefringent interference polarizer, and more particularly to a multilayer coextruded polymeric device which can be designed to polarize selected wavelengths of light by constructive optical interference.
Birefringent polarizers are generally known in the art and have been used in the past to polarize and filter selected wavelengths of light. For example, birefringent polarizers may be used to reject (reflect) specific polarized narrow wavelength ranges while transmitting the remainder of the incident light, to reduce glare from other light sources, and to act as beam splitters.
Many naturally occurring crystalline compounds act as birefringent polarizers. For example, calcite (calcium carbonate) crystals have well known birefringent properties. However, single crystals are expensive materials and cannot be readily formed into the desired shapes or configurations which are required for particular applications. Others in the art, such as Makas, U.S. Pat. No. 3,438,691, have fabricated birefringent polarizers from plate-like or sheet-like birefringent polymers such as polyethylene terephthalate incorporated into an isotropic matrix polymer.
In many instances, polymers can be oriented by uniaxial stretching to orient the polymer on a molecular level such as taught by Rogers et al, U.S. Pat. No. 4,525,413. Multilayer optical devices comprising alternating layers of highly birefringent polymers and isotropic polymers having large refractive index mismatches have been proposed by Rogers et al. However, the Rogers et al device requires the use of specific highly birefringent polymers having certain mathematical relationships between their molecular configurations and electron density distributions.
Accordingly, there remains a need in the art for birefringent interference polarizers which can be readily produced using existing techniques and readily available materials. Further, there still exists a need in the art for birefringent interference polarizers which absorb little light. Further, the need exists in the art for birefringent polarizers which can be fabricated to polarize light of specific wavelengths as desired.